This invention relates to the blending of flowable materials and, more particularly, to the blending of carrier and toner particles in development systems for continuous electrostatic processors.
In a conventional electrostatic printing process of the type disclosed in Carlson U.S. Pat. No. 2,297,691 on "Electrophotography", a uniformly charged photoreceptor is selectively discharged in an imagewise configuration to provide a latent electrostatic image which is then developed through the application of a finely divided, resinous, electroscopic marking material, called "toner". That process has enjoyed outstanding commercial success, especially in continuous copiers and duplicators (hereinafter collectively referred to as "processors") wherein the toner is applied to the latent image on the fly as the photoconductor moves through a development zone. Nevertheless, substantial effort and expense are still being devoted to the perfection of various aspects of the process, including the development step.
Generally, the toner is transported from a sump to the development zone in triboelectric combination with a relatively coarse, granular "carrier" material, such as glass, sand or ferrite beads. Indeed, that mixture is what is commonly referred to as "developer". During the development process, toner particles are electrostatically stripped from the carrier particles, thereby leaving a residue of partially denuded carrier.
In continuous processors, the partially denuded carrier is returned to the sump for recirculation and fresh toner is manually or automatically added thereto from time-to-time to maintain the toner concentration of the developer at a suitably high level. Ideally, of course, the additional or fresh toner is rapidly blended in with the recirculating developer and brought into appropriate triboelectric relationship with the carrier. Experience has, however, demonstrated that that is difficult to accomplish.